A Raman and infrared spectroscopic study of the uranyl silicates--weeksite, soddyite and haiweeite: part 2

Raman spectroscopy has been used to study the molecular structure of a series of selected uranyl silicate minerals including weeksite K2[(UO2)2(Si5O13)].H2O, soddyite [(UO2)2SiO4.2H2O] and haiweeite Ca[(UO2)2(Si5O12(OH)2](H2O)3 with UO2(2+)/SiO2 molar ratio 2:1 or 2:5. Raman spectra clearly show well resolved bands in the 750-800 cm(-1) region and in the 950-1000 cm(-1) region assigned to the nu1 modes of the (UO2)2+ units and to the (SiO4)4- tetrahedra. Soddyite is characterized by Raman bands at 828.0, 808.6 and 801.8 cm(-1), 909.6 and 898.0 cm(-1), and 268.2, 257.8 and 246.9 cm(-1), attributed to the nu1, nu3, and nu2 (delta) (UO2)2+, respectively. Coincidences of the nu1 (UO2)2+ and the nu1 (SiO4)4- is expected. Bands at 1082.2, 1071.2, 1036.3, 995.1 and 966.3 cm(-1) are attributed to the nu3 (SiO4)4-. Sets of Raman bands in the 200-300 cm(-1) region are assigned to nu2 (delta) (UO2)2+ and UO ligand vibrations. Multiple bands indicate the non-equivalence of the UO bonds and the lifting of the degeneracy of nu2 (delta) (UO2)2+ vibrations. The (SiO4)4- tetrahedral are characterized by bands in the 470-550 cm(-1) and in the 390-420 cm(-1) region. These bands are attributed to the nu4 and nu2 (SiO4)4- bending modes. The minerals show characteristic OH stretching bands in the 2900-3500 and 3600-3700 cm(-1).     

An infrared and Raman spectroscopic study of the uranyl micas

Vibrational spectroscopy using a combination of infrared and Raman spectroscopy has been used to study the uranyl micas also known as the autunite minerals, of general formula M(UO2)2(XO4)2.8-12H2O where M may be Ba, Ca, Cu, Fe2+, Mg, Mn2+ or 1/2(HAl) and X is As or P. Included in these minerals are autunite, metautunite, torbernite, meta-torbernite, meta-zeunerite, saléeite and sabugalite. Compared with the results of infrared spectroscopy, Raman microscopy shows excellent band separation enabling the separation and identification of bands attributed to (UO2)2+ units, PO4 and AsO4 units. Common to all spectra were bands at around 900 and 818 cm(-1), attributed to the antisymmetric and symmetric stretching vibrations of the (UO2)2+ units. Water in autunites is in a highly structured arrangement in the interlayer of the uranyl micas. Water molecules are differentiated according to the strength of the hydrogen bonds formed between the water and the adjacent uranyl-phosphate or uranyl-arsenate surfaces and the hydration sphere of the interlayer cation.     

A Raman spectroscopic study of the uranyl sulphate mineral johannite

Raman spectroscopy at 298 and 77K has been used to study the secondary uranyl mineral johannite of formula (Cu(UO2)2(SO4)2(OH)2 x 8H2O). Four Raman bands are observed at 3593, 3523, 3387 and 3234cm(-1) and four infrared bands at 3589, 3518, 3389 and 3205cm(-1). The first two bands are assigned to OH- units (hydroxyls) and the second two bands to water units. Estimations of the hydrogen bond distances for these four bands are 3.35, 2.92, 2.79 and 2.70 A. A sharp intense band at 1042 cm(-1) is attributed to the (SO4)2- symmetric stretching vibration and the three Raman bands at 1147, 1100 and 1090cm(-1) to the (SO4)2- anti-symmetric stretching vibrations. The nu2 bending modes were at 469, 425 and 388 cm(-1) at 77K confirming the reduction in symmetry of the (SO4)2- units. At 77K two bands at 811 and 786 cm(-1) are attributed to the nu1 symmetric stretching modes of the (UO2)2+ units suggesting the non-equivalence of the UO bonds in the (UO2)2+ units. The band at 786cm(-1), however, may be related to water molecules libration modes. In the 77K Raman spectrum, bands are observed at 306, 282, 231 and 210cm(-1) with other low intensity bands found at 191, 170 and 149cm(-1). The two bands at 282 and 210 cm(-1) are attributed to the doubly degenerate nu2 bending vibration of the (UO2)2+ units. Raman spectroscopy can contribute significant knowledge in the study of uranyl minerals because of better band separation with significantly narrower bands, avoiding the complex spectral profiles as observed with infrared spectroscopy.     

A Raman spectroscopic study of the uranyl phosphate mineral threadgoldite

Raman spectra of threadgoldite at 298 and 77K are measured and interpreted for the first time. Bands related the (UO(2))(2+) and (PO(4))(3-) stretching and bending vibrations are tenatively attributed together with the bands assigned to the stretching a and bending vibrations of water molecules and hydroxyls. Hydrogen-bonding network and H(2)O and (OH)(-1) libration modes are mentioned. U-O bond lengths in uranyls are calculated via empirical relations R(U-O)=f[nu(1) and nu(3)(UO(2))(2+)]A. They are comparable to the values inferred from the single crystal structure analysis of threadgoldite.     

A Raman spectroscopic study of the uranyl phosphate mineral bergenite

Raman spectroscopy at 298 and 77 K of bergenite has been used to characterise this uranyl phosphate mineral. Bands at 995, 971 and 961 cm-1 (298 K) and 1006, 996, 971, 960 and 948 cm-1 (77K) are assigned to the nu1(PO4)3- symmetric stretching vibration. Three bands at 1059, 1107 and 1152 cm-1 (298 K) and 1061, 1114 and 1164 cm-1 (77 K) are attributed to the nu3(PO4)3- antisymmetric stretching vibrations. Two bands at 810 and 798 cm-1 (298 K) and 812 and 800 cm-1 (77 K) are attributed to the nu1 symmetric stretching vibration of the (UO2)2+ units. Bands at 860 cm-1 (298 K) and 866 cm-1 (77 K) are assigned to the nu3 antisymmetric stretching vibrations of the (UO2)2+ units. UO bond lengths in uranyls, calculated using the wavenumbers of the nu1 and nu3(UO2)2+ vibrations with empirical relations by Bartlett and Cooney, are in agreement with the X-ray single crystal structure data. Bands at (444, 432, 408 cm-1) (298 K), and (446, 434, 410 and 393 cm-1) (77 K) are assigned to the split doubly degenerate nu2(PO4)3- in-plane bending vibrations. The band at 547 cm-1 (298 K) and 549 cm-1 (77 K) are attributed to the nu4(PO4)3- out-of-plane bending vibrations. Raman bands at 3607, 3459, 3295 and 2944 cm-1 are attributed to water stretching vibrations and enable the calculation of hydrogen bond distances of >3.2, 2.847, 2.740 and 2.637 A. These bands prove the presence of structurally nonequivalent hydrogen bonded water molecules in the structure of bergenite.     

A Raman spectroscopic study of the uranyl tellurite mineral schmitterite

Raman spectra of schmitterite measured at 298 and 77K are presented and discussed in detail and in part in comparison with published IR spectrum of synthetic schmitterite. U-O bond lengths in uranyls, calculated with the empirical relations R(U-O)=f[nu(1)(UO(2))(2+)]A and R(U-O)=f[nu(3)(UO(2))(2+)] A, are close to those inferred from the X-ray single crystal structure of synthetic schmitterite and agree also with the data for other natural and synthetic uranyl tellurites.     

A Raman and infrared spectroscopic study of the phosphate mineral laueite

A laueite mineral sample from Lavra Da Ilha, Minas Gerais, Brazil has been studied by vibrational spectroscopy and scanning electron microscopy with EDX. Chemical formula calculated on the basis of semi-quantitative chemical analysis can be expressed as (Mn²⁺_0.85,Fe²⁺_0.10Mg_0.05)_∑1.00(Fe³⁺_1.90,Al_0.10)_∑2.00(PO₄)₂(OH)₂·8H₂O.The laueite structure is based on an infinite chains of vertex-linked oxygen octahedra, with Fe³⁺ occupying the octahedral centers, the chain oriented parallel to the c-axis and linked by PO₄ groups. Consequentially not all phosphate units are identical. Two intense Raman bands observed at 980 and 1045 cm⁻¹ are assigned to the ν₁ PO₄³⁻ symmetric stretching mode. Intense Raman bands are observed at 525 and 551 cm⁻¹ with a shoulder at 542 cm⁻¹ are assigned to the ν₄ out of plane bending modes of the PO₄³⁻. The observation of multiple bands supports the concept of non-equivalent phosphate units in the structure. Intense Raman bands are observed at 3379 and 3478 cm⁻¹ and are attributed to the OH stretching vibrations of the hydroxyl units. Intense broad infrared bands are observed. Vibrational spectroscopy enables subtle details of the molecular structure of laueite to be determined.     

Raman,resonance Raman and infrared spectra of potassium uranyl croconate

The Raman, resonance Raman and IR spectra of potassium uranyl croconate, UO₂(H₂O)K₂(C₅O₅)₂ were obtained and interpreted. Several croconate modes are split indicating a substantial decrease in the oxocarbon symmetry, as is to be expected from a recent crystallographic investigation, revealing the coordination of the oxocarbon to be two non-equivalent UO²⁺₂ moieties in a monodentate fashion. In terms of vibrational frequency shifts it can be concluded that the UO²⁺₂ moiety behaves as an isolated oscillator.The resonance Raman results suggest that the strong band centered around 450 nm in the UV—vis spectrum should be assigned to a charge transfer transition from the oxocarbon to the uranyl ion. In fact, as resonance is approached, both uranyl and croconate modes are enhanced. It can also be inferred that the chromophore is rather delocalized into the oxocarbon ring, rather than localized in the carbonyl groups as previously observed for other croconate complexes.     

Hydrated double carbonates – A Raman and infrared spectroscopic study

The Raman spectra of selected double carbonates including pirssonite, gaylussite, shortite and quintinite complemented with infrared spectra have been used to characterise the structure of these carbonate minerals. By using a Libowitzky type function hydrogen bond distances for these minerals of 2.669–2.766 Å are estimated. The variation in the hydrogen bond distances contributed to the stability of the mineral. The Raman spectrum of pirssonite shows a single band at 1080 cm⁻¹ attributed to the (CO₃)²⁻ symmetric stretching mode, in contrast to shortite and quintinite where two bands are observed. Multiple bands are observed for the antisymmetric stretching and bending region for these minerals proving that the carbonate unit is distorted in the structure of pirssonite and gaylussite.     

An infrared and resonance Raman spectroscopic study of phenylazonaphthol pigments

The IR, resonance Raman (RR) and electronic spectra of two phenylazonaphthol pigments, LRC Scarlet and 4BL Red, have been measured and assignments of the vibrational and electronic spectra were facilitated by ab initio calculation s at the B3-LYP/DZ level. Vibrational spectra indicate that the major species in the solid state are the hydrazo tautomers. Electronic spectra are in accordance with the nature of the electronic transitions predicted by time-dependent B3-LYP/DZ calculations.     

An infrared and Raman spectroscopic study of natural zinc phosphates

Zinc phosphates are important in the study of the phosphatisation of metals. Raman spectroscopy in combination with infrared spectroscopy has been used to characterise the zinc phosphate minerals. The minerals may be characterised by the patterns of the hydroxyl stretching vibrations in both the Raman and infrared spectra. Spencerite is characterised by a sharp Raman band at 3516 cm(-1) and tarbuttite by a single band at 3446 cm(-1). The patterns of the Raman spectra of the hydroxyl stretching region of hopeite and parahopeite are different in line with their differing crystal structures. The Raman spectrum of the PO4 stretching region shows better band separated peaks than the infrared spectra which consist of a complex set of overlapping bands. The position of the PO4 symmetric stretching mode can be used to identify the zinc phosphate mineral. It is apparent that Raman spectroscopy lends itself to the fundamental study of the evolution of zinc phosphate films.     

Raman and infrared spectroscopic study of the anhydrous carbonate minerals shortite and barytocalcite

The Raman spectra of shortite and barytocalcite complimented with infrared spectra have been used to characterise the structure of these carbonate minerals. The Raman spectrum of barytocalcite shows a single band at 1086cm(-1) attributed to the (CO(3))(2-) symmetric stretching mode, in contrast to shortite where two bands are observed. The observation of two bands for shortite confirms the concept of more than one crystallographically distinct carbonate unit in the unit cell. Multiple bands are observed for the antisymmetric stretching and bending region for these minerals proving that the carbonate unit is distorted in the structure of both shortite and barytocalcite.     

A Raman spectroscopic study of N,N-dimethylacrylamide

A comprehensive Raman spectroscopic study of N,N-dimethylacrylamide has been carried out to produce new vibrational assignments for the molecule. The provision of polarization data for the first time has enabled the correction of several assignments for the normal modes previously reported in the literature to be made.     

An infrared and Raman spectroscopic study of some metal pyridine tetracyanonickelate complexes

The results of an infrared and Raman spectroscopic study are presented for seven new metal pyridine tetracyanonickelate complexes, M(py)₂Ni(CN)₄, M = Mn, Co, Fe, Ni, Cu, Zn and Cd. It is shown that the spectra are consistent with a proposed crystal structure for these complexes derived from X-ray diffraction measurements. The spectra can be clearly distinguished from those of analogous Hofmann-type clathrates with which the nickel complex had been previously confused. The copper complex has spectral features different from the other six compounds and an explanation is proposed in terms of a distortion of the general crystal structure due to the Jahn-Teller effect. Analysis of the single, sharp bands of coordinated pyridine offers a method of resolving some difficulties in earlier assignments of the normal modes of the free base. Several modes of coordinated pyridine have upward shifts in frequency compared to those in the free molecule and the shifts are metal dependent. An explanation, supported by a simple normal coordinate analysis on a model, is provided in terms of coupling with low frequency vibrations, particularly the M-N stretching frequency. Other vibrations of the Ni(CN)₄ group, which coordinates to the metals M to form a two-dimensional coordination polymer, are also metal dependent. It is similarly suggested that coupling with low frequency modes is the principal cause of the upward shifts in frequency.     

A Raman spectroscopic study of synthetic giniite

The mineral giniite has been synthesised and characterised by XRD, SEM and Raman and infrared spectroscopy. SEM images of the olive-green giniite display a very unusual image of pseudo-spheres with roughened surfaces of around 1-10microm in size. The face to face contact of the spheres suggests that the spheres are colloidal and carry a surface charge. Raman spectroscopy proves the (PO4)3- units are reduced in symmetry and in all probability more than one type of phosphate unit is found in the structure. Raman bands at 77K are observed at 3380 and 3186cm-1 with an additional sharp band at 3100cm-1. The first two bands are assigned to water stretching vibrations and the latter to an OH stretching band. Intense Raman bands observed at 396, 346 and 234cm-1are attributed to the FeO stretching vibrations. The giniite phosphate units are characterised by two Raman bands at 1023 and 948cm-1 assigned to symmetric stretching mode of the (PO4)3- units. A complex band is observed at 460.5cm-1 with additional components at 486.8 and 445.7cm-1 attributed to the nu(2) bending modes suggesting a reduction of symmetry of the (PO4)3- units.     

Fourier-transform Raman and infrared spectroscopic analysis of dipyrrinones and mesobilirubins

The Fourier-transform Raman (FT-Raman), infrared (FT-IR), and UV-visible absorption spectra of four dipyrrinones and two mesobilirubins have been investigated in the solid state and in CH2Cl2 solutions. A detailed spectral analysis, assignment and discussion of these spectra are presented. The bands at 1735-1738, 1691-1707 and 1359-1377 cm(-1) which were assigned to the stretching vibrations of the C-O-C and C-O-H and symmetric deformation of C-H bonds, respectively, can act as a marker to distinguish the compounds of this class. The striking differences between the spectra of the compounds suggest that mesobilirubin XIIIalpha is tending to adopt as ridge-tile conformation, rather than linear conformation.     

Raman and infrared spectroscopic investigation of the cation distributions in amphiboles

Micro-Raman spectra of a series of amphiboles have allowed an analysis of the cation distributions to be made. In addition, the micro-infrared absorption spectrum of Cummingtonite, one mineral in the series, has made possible the determination of both principal and interaction OH force constants. The results are interpreted in terms of the electronegativities of the cations occupying nearby sites.     

A thermogravimetric and infrared emission spectroscopic study of alunite

Thermogravimetric and differential thermogravimetric analysis has been used to characterize alunite of formula [K₂(Al³⁺)₆(SO₄)₄(OH)₁₂]. Thermal decomposition occurs in a series of steps (a) dehydration up to 225°C, (b) well defined dehydroxylation at 520°C and desulphation which takes place as a series of steps at 649, 685 and 744°C.The alunite minerals were further characterized by infrared emission spectroscopy (IES). Well defined hydroxyl stretching bands at around 3463 and 3449 cm^?1 are observed. At 550°C all intensity in these bands is lost in harmony with the thermal analysis results. OH stretching bands give calculated hydrogen bond distances of 2.90 and 2.84–7 Å. These hydrogen bond distances increase with increasing temperature. Characteristic (SO₄)^2? stretching modes are observed at 1029.5, 1086 and 1170 cm^?1. These bands shift to lower wavenumbers on thermal treatment. The intensity in these bands is lost by 550°C.     

Fourier-transform Raman and infrared spectroscopic analysis of novel biliverdin compounds

The vibrational spectroscopy of novel biliverdin compounds were studied by Fourier-transform Raman (FT-Raman) and infrared (FT-IR) spectroscopy. The effects of type, length and position of substituents at C(8) and C(12) or C(1) and C(19) of tetrapyrroles on FT-Raman and FT-IR spectra of these compounds, are discussed. The marker bands are developed in order to distinguish between etiobiliverdin and mesobiliverdin.     

An infrared and Raman spectroscopic study of polyanilines co-doped with metal ions and H+

Polyanilines doped with (HCl+KCl) and (HCl+CoCl2) were prepared by co-doping method, respectively. For comparison, polyaniline emeraldine salt (ES) by doping with HCl and its emeraldine base (EB) form were also synthesized. The co-doped polyanilines, ES and EB samples were all characterized by Fourier transform infrared spectroscopy (FTIR) and Raman spectroscopy aiming to understand the transformations in the different doping status. The results show that the doping degree of K+ ions is considerably higher than that of Co2+ ions under the same co-doping conditions possibly due to different pseudoprotonation constants of EB with K+ ions and Co2+ ions. Moreover, morphology difference of polyaniline co-doped with alkaline metal ions or transition meal ions may arise from different coordination geometry of metal ions. Nevertheless, there are similar chemical transformations of quinoid units to benzenoid ones on polyaniline backbones for the ES and both co-doped samples. And the polyaniline backbones co-doped with H+ and metal cations are found to attain weaker charge delocalization than the ES which is doped solely with H+.